Weird light issue. Need help please

Thats simply not true.

A light emmitting *diode* is by definition a solid state one way "choke" valve for the electricity flow.

IF it works in both polarity directions on dc, thats simply because they doubled up the leds, 1/2 one direction, 1/2 the other direction.

 

well dang it now I'm gonna have to pull one out and try!

 

how do I always seem to plug them in the right way first! I'm not that lucky. or maybe I'm dreaming

 

If they work both ways, you have alternating current, on a truck, that means you have some low grade positive leakage to ground. If this is the case, you will probably notice that one direction is brighter than the other.

Leds require very little in the way of current flow to power them, so a tiny amountnof leakage is all it needs

 

If you want proof that the led is a choke, take 2 working leds, make a circuit that has them in series, place one in the correct orientation, then turn the second one around (wromg orientation)

Neither should light up, as if they were a blown incandesent.

Reverse orientation of the 2nd and both will light up.

For accessible examples of this in the world, remember the old crappy led christmas light strings? One bulb would be broken or loose, or worse, was put in backwards and 1/2 the string wouldnt work because they passed the current through the bulb before continuing that wire as opposed to tapping 2 wires with the same socket (the way most trucks are wired)

 

they require very low amperage but are voltage sensitive aren't they? An incandescent light will get dimmer and dimmer as voltage drops, will an LED do the same

And I'm not disputing what you are saying at all. clearly you know more about it than I.. I am pretty good and building and fixing DC stuff, I know how most of it works but not always why..

 

@Iester is not crazy. I have encountered led marker lights that are lead neutral and will work either way. Both in Grote and Trucklight. They just need a solid ground. Those type usually have red and black wires and the brightness will differ on which wire has been made 12v. Some of the lights sold by United Pacific are polarity specific. In that case the white wire is usually ground and black is 12v.

 

Back to the original question, because he is working with strobes I wonder if it had to do with syncing, or the pattern changing. Those that I have used have also had a yellow wire for syncing multiple lights together, as well as a blue wire for pattern changes.

 

Leds pull very minimal current, correct, its usually in the milliampere realm.

They also have a voltage range, under which they just dont emit, above which they tend to burn out. Its roughly 1 to 5 volts, there is usually a voltage drop circuit for them to handle the "12v" input, but this is what gets fried if it goes too high

As they get close to their minimum voltage, if they are designed with voltage sensing, they will dim like incandescents, if they dont have that, they will dim but only right near their voltage threshold



Im not saying your wrong that youve been able to get some to work in both polarities, but whats being done there on the leds circuit-board is much more complex and usually cost prohibitive to be the norm. If you are buying high dollar leds though i guess it wouldnt be a surprise.

 

If it is a newer truck, I wonder if the wires are multiplexed (computer controlled). If the system doesn’t see enough of a load on the line then it assumes there’s a problem and shuts down the line. LEDs draw far less current, perhaps try a load resistor across the leads.